|Update October 2005 from Annemiek Schilder, Dept. Plant Pathology, Michigan State University
Dormant applications of crop protection chemicals are typically applied in the fall or spring when no green tissue is present on plants. The purpose of dormant sprays is to eradicate pathogens and insects that are overwintering on the plant. Lime sulfur (a mixture of calcium polysulfides formed by boiling slaked lime with sulfur) has long been used as a dormant spray in tree fruit and brambles. Copper formulations are also used, particularly for control of bacterial diseases. These products kill mainly through direct contact, so applications must be applied with maximum coverage. Lime sulfur, while effective, is smelly, corrosive to farm equipment, and can be phytotoxic to green tissues. While lime sulfur used to be relatively inexpensive, the price has gone up significantly in recent years and can be as high as $100 per acre if applied at higher rates.
In grapes we have done several years of trials with dormant fungicide applications, including less expensive alternatives, such as sulfur and copper products. Below a graph showing the efficacy of a single dormant spray at budswell against Phomopsis rachis infection in Niagara grapes at harvest. The following products were tested: Microfine Sulfur (powdered sulfur), Sulfur 6L (liquid sulfur), Kocide 2000 (copper hydroxide), and Cuprofix (basic copper sulfate). No other fungicides were applied during the season. ProPhyt applied on a seasonal schedule was included for comparison. We also found that dormant applications of sulfur and copper reduced black rot infection of fruit, and that dormant copper reduced downy mildew infection. In general, dormant sprays significantly reduce disease pressure of a range of diseases. The effects of dormant sprays on powdery mildew infection will be investigated in 2005.